Technical Field
The present application relates to a switch mode power supply, and in particular, to an alternating current (AC)-direct current (DC) conversion circuit and a control method thereof.
Related Art
A single-stage power factor (Power Factor, PF for short) corrector in the soft switching technologies, active clamping flyback, and active clamping forward, and improvement solutions thereof are widely used in power supplies. U.S. Pat. No. 7,301,785 B2 discloses a switching power supply circuit, and a voltage stress of a primary side switching transistor of the transformer circuit changes with the state of load and shifts to an excessively high voltage stress when the state is full load. U.S. Pat. No. 7,301,785 B2 fails to fundamentally overcome disadvantages of typical resonance technologies. Therefore, an available power range and input and output voltage ranges are limited. Chinese patent CN101692595B discloses an active clamping forward-flyback circuit. Upon comparison, the circuit is improved on the basis of other disclosed circuits. However, for the requirements of AC rectification and filtering, although a first secondary side of the circuit may not need a large-capacity electrolytic capacitor, the secondary side still needs an additional high-frequency filter capacitor in practical applications. An AC input side also needs to use a full bridge rectifier. A second secondary side rectifier circuit is complex. In an input rectifier loop or an output rectifier loop, a loss of a plurality of series-connected diodes is relatively large. Meanwhile, when the circuit does not include a large-capacity electrolytic capacitor, output voltage and current waves are both large. In practical applications, the circuit can be hardly applied to a scenario of an AC-DC conversion circuit with large power, and it is relatively appropriate to apply the circuit to a scenario of DC-DC conversion. Besides, when an AC is input to the transformer, a periodic change of an input voltage causes a change of a corresponding drive duty factor. Therefore, a loss of a clamping circuit increases in a low voltage input part increases due to the reason that a resonance condition is not met, and the stability and reliability of the circuit are reduced.